Embodiments of the invention relate to a guard for an electrostatic chuck that is used to hold a substrate in a plasma during processing.
In the fabrication of electronic circuits and displays, semiconductor, dielectric, or conductor materials are formed on a substrate, such as a silicon wafer or glass. The materials are typically formed by chemical vapor deposition (CVD), physical vapor deposition (PVD), oxidation, or nitridation processes. Thereafter, the materials are etched to form features such as gates, vias, contact holes and interconnect lines. In a typical etching process, a patterned mask of photoresist or oxide hard mask is formed on the substrate by photolithography, and a plasma etches exposed portions of the substrate. The plasma is an electrically conductive gaseous medium formed by inductively or capacitively coupling RF energy into a process gas.
The processes described above are typically carried out in a substrate processing apparatus that comprises a process chamber. The process chamber comprises an electrostatic chuck to hold the substrate in a process zone of the chamber. The electrostatic chuck comprises a dielectric that covers an electrode, the dielectric having a receiving surface to receive the substrate. A process gas is introduced into the chamber and the process gas is energized into a plasma to process the substrate. However, the plasma often damages the electrostatic chuck, especially by eroding a periphery of the electrostatic chuck or undesirably depositing process residues along the periphery. When the periphery comprises parts having convoluted surface topographies with crevices and small projections, this problem may be particularly acute. Additionally, if parts of the electrostatic chuck along the periphery are biased at a high voltage, electrical shorts into the plasma may occur.
Yet another problem is when the substrate is not properly aligned on the receiving surface of the electrostatic chuck. Such misalignment of the substrate can cause uneven processing. Misalignment often occurs during placement of the substrate on the receiving surface. The substrate can also shift during processing due to mechanical vibrations or non-uniform gas pressures. Such shifting of the substrate on the receiving surface can cause flaking of the process residues deposited on the electrostatic chuck.
One version of electrostatic chuck 10 comprises a protective guard 15 along the periphery 20 to protect the periphery 20 from the plasma, as illustrated in FIG. 1 (Prior Art). For example, the guard 15 may comprise a ceramic annulus that curves over the periphery 20 of the electrostatic chuck 10 to isolate the periphery 20 from the ambient plasma. Additionally, the guard 15 may comprise a ridge 25 near the substrate-receiving surface 30 to prevent excessive displacement of the substrate 35. The ridge 25 forms a tall, circular, upward protrusion from the guard 15.
However, a problem with such a protective guard 15 is that process residues 45 that deposit on the guard 15 can flake off and contaminate the process zone 40 as well as the substrate 35. Flaking increases as the thickness of the deposited process residues 45 increases. Process residues 45 also flake off when temperature fluctuations occur and cause layers of the process residues 45 having different thermal expansion coefficients to delaminate. Additionally, the tall ridge 25 is easily eroded by the plasma, shortening the operational lifetime of the guard 15. Such erosion can also cause flaking of the process residues 45 from the ridge 25, which then contaminate the substrate 35.
Thus, it is desirable to have a guard for an electrostatic chuck that can substantially prevent contamination by process residues. It is further desirable to have an electrostatic chuck guard with an increased operational lifetime. It is still further desirable to have an electrostatic chuck guard capable of maintaining proper placement of the substrate on the receiving surface of the electrostatic chuck.